Summary Core B NME Mouse Core Our published studies suggest that mice with more physiological exposure to natural mouse microbes have immune systems that are a better match for the immune system in humans: In contrast to typical ?clean? laboratory mice (which are maintained in barrier facilities to avoid pathogen exposure) these ?dirty? mice ? also called normal microbial experience (NME) mice ? may therefore be more useful to model the characteristics and function of the human immune system, including the maintenance and breakdown of immune tolerance. The goal of this NME Mouse Core is to reliably and cost-effectively produce NME animals that can be used by the Projects in this P01, including careful quality control of these animals to make sure that they are suitably well defined for interpretable studies.